Engines, including diesel engines, gasoline engines, gaseous fuel-driven engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of gaseous and solid material, including particulate matter, nitrogen oxides (NOx), and sulfur compounds.
Due to heightened environmental concerns, exhaust emission standards have become increasingly stringent over the years. The amount of pollutants emitted from an engine may be regulated depending on the type, size, and/or class of engine.
One method that has been implemented by engine manufacturers to comply with the regulation of engine emissions includes introducing a catalyst in the exhaust stream. Some catalysts are capable of removing pollutants from the exhaust gas by chemical reaction. For example, some catalysts provide a catalytic reduction of NOx in the exhaust gas by reacting NOx with ammonia, which is injected into the exhaust gas stream upstream from the catalyst. Therefore, ammonia or urea, which may be converted into ammonia, must be stored and used when needed for catalytic reduction of NOx. The storage of such chemicals is costly, requires constant replenishment, and may require specialized storage equipment. Further, storage of ammonia is hazardous because of its high reactivity.
Another method that has been implemented by engine manufacturers to comply with engine emissions regulations is exhaust gas recirculation (“EGR”). EGR systems recirculate engine exhaust gas into the intake air supply of the engine. The exhaust gas directed to the engine cylinder reduces the concentration of oxygen within the cylinder and increases the specific heat of the air/fuel mixture, thereby lowering the maximum combustion temperature within the cylinder. The lowered maximum combustion temperature and reduced oxygen concentration can slow the chemical reaction of the combustion process and decrease the formation of NOx.
For example, an EGR system is described in U.S. Pat. No. 5,794,445 (“the '445 patent”) to Dungner. The '445 patent describes an EGR system in which a portion of exhaust gas from a first cylinder group is used to drive an EGR turbine and a portion of the exhaust gas from a second cylinder group is compressed by an EGR compressor, which is driven by the EGR turbine. The portion of the exhaust gas that is compressed by the EGR compressor is cooled by an exhaust gas cooler downstream from the EGR compressor before being sent to an inlet side of an engine where the compressed recirculated exhaust gas combines with compressed air from a main compressor.
Although the '445 patent discloses an EGR system for decreasing NOx emissions, there is a risk of exhaust system component corrosion due to the presence of acidic sulfur by-products in the exhaust stream. The EGR system includes an exhaust gas cooler downstream from the EGR compressor. Cooling compressed exhaust gas allows the formation of sulfuric acid, and therefore, the exhaust gas cooler and any other components downstream from the exhaust gas cooler are vulnerable to corrosion.
Sulfur is a naturally occurring element in all crude oils. Heavy fuels derived from crude oil typically have higher sulfur content. Diesel fuels, for example, often contain sulfur and other substances that, at times, convert to potentially corrosive and environmentally unfriendly by-products. During combustion, sulfur is oxidized to sulfur dioxide (SO2) and minute amounts of sulfur trioxide (SO3). The resulting SO3 reacts with water vapor to form sulfuric acid. Once the exhaust gas cools, the resulting SO2 likewise reacts with water condensate to form sulfuric acid. The sulfuric acid subsequently condenses downstream in the exhaust system to produce an acidic condensate.
Acidic condensates are a major cause of engine component corrosion, secondary wear from corrosion by-products, and engine oil acidification. Additionally, high sulfur fuel and its resulting acidic condensate can affect the performance and durability of combustion engine systems and their components, such as, e.g., EGR systems, after-cooler systems (e.g., an air-to-air after-cooler (“ATAAC”) and the like), turbocharger compressors, sensors, catalysts, and the like.
After-cooling involves cooling engine intake, e.g., ambient air, after compression and prior to introduction into a cylinder of the engine. After-cooling the engine intake provides an increase in engine power and lower NOx emissions. However, engine system components that include after-cooling systems positioned in the exhaust stream are vulnerable to corrosion since the exhaust stream includes substances that, when compressed, form sulfuric acid.
The disclosed system is directed to overcoming one or more of the problems set forth above.